Session: 11-08-01: Fundamentals of Phase-Change Including Micro/Nanoscale Effects-Boiling, Evaporation, Freezing and Condensation

Paper Number: 95846

95846 - Critical Heat Flux Enhancement on Cylindrical Tubes With Circumferential Micro-Channels During Saturated Pool Boiling of Water 

Boiling heat transfer plays an important role in numerous industrial applications critical to modern society. Additionally, it is widely accepted that the realization of next-generation high power electronics and photonic systems are strongly depended on substantial enhancement in cooling capacities using boiling heat transfer. However, this cooling capacity is inherently limited by the critical heat flux (CHF) point. CHF is the maximum heat transfer capability of a system beyond which a rapid inflation of cooling surface temperature occurs leading to catastrophic failure of the system. There is a mounting evidence that boiling CHF can be significantly improved by altering the morphology of the heat transfer surface using engineered structures. Specifically, the improvements have been possible through the utilization of micro- and nano-scale features including nanostructures, micropillars, microchannels, hierarchical structures, and many others. However, this massive heat transfer enhancement using water as the working fluid has been focused primarily on the flat surfaces. Although several researchers have attempted the boiling enhancement on engineered tubular surfaces, the experiments are limited to low heat flux values through the utilization of various refrigerants as the working fluid or up to the heater power for water. As such, this work experimentally characterizes the pool boiling heat transfer enhancement of cylindrical tubes with circumferential micro-channels using saturated water as the working fluid. Three different micro-channel geometries were machined on copper cylinders using CNC. The channels had a fixed width of approximately 410 µm and a fixed depth of approximately 400 µm. The three different tubes fabricated in this work had fin widths of 300 µm, 600 µm and 900 µm. The active heating area on the cylindrical tubes had a dimension of 10 mm diameter and 10 mm length. Two alumina insulation tubes were used to define the heater length of microchannel tubes. A custom-built cylindrical heater was designed using a nichrome wire coil of 30 AWG with a resistance of 19.57 Ω/inch of coil to provide joule heating to the engineered tubes. The electrical wire was insulated from the copper heater using a thin layer of alumina paste. A 10 kW DC power supply was used to resistively heat the nichrome wire and four thermocouples were circumferentially embedded in the copper tube to measure the average surface temperature during boiling. The saturated pool boiling tests up to CHF were conducted at atmospheric pressure using water as the working fluid. While a CHF of 70 W/cm² has been achieved for the plain copper tube, the cylindrical tubes with microchannel geometries show more than 70% enhancement of CHF for saturated pool boiling of water at atmospheric pressure.

Presenting Author: Omar Hernandez Rodriguez Aerospace Center (cSETR), The University of Texas at El Paso

Presenting Author Biography: M.A. Omar Hernandez Rodriguez is currently a Ph.D. student in the Department of Aerospace and Mechanical Engineering at The University of Texas at El Paso (UTEP). He received his first M.S. in Physics from UTEP in 2018 and second M.S. in Mechanical Engineering from UTEP in 2020. He completed his Bachelor in Engineering Physics from the Autonomous University of Ciudad Juarez (UACJ) in 2015. His doctoral research is focused on surface engineering and advanced diagnostics to characterize the enhancement mechanisms during high-pressure boiling heat transfer.

Authors:

Omar Hernandez Rodriguez Aerospace Center (cSETR), The University of Texas at El Paso
Md Mahamudur Rahman Aerospace Center (cSETR), The University of Texas At El Paso (UTEP)